Studies in this laboratory have determined that a large dose of ovalbumin (100 mg) injected i.v. two days earlier directly influenced small dense thymocytes to undergo blast transformation, followed by massive emigration of large low density cells from the thymus cortex to the splenic marginal zone-red pulp. This antigen induced migratory pathway is superimposed upon a normal pathway taken by far fewer large low density cortical thymocytes to these sites. This newly described pathway is independent of that taken by small dense thymocytes to the periarteriolar lymphoid sheath (classical thymus dependent area) which is apparently uninfluenced by antigen. In contrast, orally administered antigen also induces blast transformation within the thymus, but, instead, induces cortical thymocytes to migrate to Peyer's patches; homing to spleen appears to be unaffected by antigen given orally. Other data indicate that in rats the Thy 1 surface marker charasteristic of bone marrow cells and cortical thymocytes, but not medullary thymocytes or any peripheral lymphocytes, appears only on large cells present in the marginal zone-red pulp areas after injection of the suppressive dose of antigen mentioned above. Likewise, Peyer's patches contain virtually no Thy 1 plus cells until given antigen orally. These cells appear in Peyer's patches by day 2. The proposed studies will attempt to establish whether the cells emigration from the thymus cortex to spleen and Peyer's patches in accelerated fashion after large i.v. or oral doses of antigen, respectively, (1) bear the Thy 1 surface marker, and (2) are destined to function as obligatory suppressor cells in the periphery. Both nonspecific and specific suppressor cell phenomena will be investigated.